1. Field of the Invention
The present invention relates to a limit switch which limits or controls a movement, and, in particular, to a constitution of a non-contact type microswitch extensively used for industrial purpose which comprises water resistance, corrosion resistance and abrasion resistance. It is to be noted that the limit switch is a switch to detect a position, a displacement, a movement, a passage and the like, and the microswitch is defined as a compact type switch designed and produced so that a switching operation to open and close an electrical current can be promptly and reliably performed with a small force.
2. Description of the Related Art
A conventional limit switch generally has an actuator of a lever type rotatably supported by a hinge, and when a free end of the actuator is pushed and moved by a cam and a dog of an operational mechanism, the movement thereof is transmitted to a slide pin, and by a snap action of a toggle mechanism and the like, a contact thereof is switched to OFF from ON or ON from OFF, so that a signal is outputted and an operation of a moving mechanism is detected.
However, since an urging force which actuates the limit switch receives resistance due to a reaction accompanied with a snap action of the contact by moving the actuator lever, an urging force large enough to overcome the resistance is required. Therefore, in order to avoid an influence, which exerts a counteraction on the function, it is better that an operating force of the limit switch is as weak as possible. Further, in bad surroundings where the limit switch is used not only for industrial machines, but also for field equipment of civil engineering, building construction and the like, abrasion due to accumulation of dust and repeated operations is unavoidable for a spindle of the hinge which supports the lever to function as the actuator. A sealed microswitch of JIS C 4508 is a large type, and is difficult to use conveniently for the places, which require a compact construction.
Therefore, the object of the present invention is to provide a general type limit switch, which has abrasive resistance, corrosion resistance and water resistance, and is excellent in durability and, moreover, can function with a weak operating force.
In order to achieve the above-described object, the limit switch according to the present invention is a flat box type housing as a basic model with a cavity concavely provided, and an outer surface of the housing comprises: two surfaces backward and forward in a thickness direction where mounting holes are piercingly provided at standard positions (a center distance between two places of mounting holes according to JIS C 4505 is: 25.4 mm) and which function as mounting surfaces; an upper surface which defines upper edges of these two surfaces and supports an actuator lever; and an under surface which defines under edges of these two surfaces and where the cavity is open, wherein a non-contact type microswitch is provided inside the cavity with upper and lower positions adjustable; and the actuator lever is supported on the upper surface by a cantilever plate spring; and a piston connecting the actuator lever and the microswitch is insertably mounted between both of them; and an annular concave portion circumference on the upper surface, where a piercing hole to fittingly mount the piston by being connected with the cavity is open, is sealed at the outer edge of the elastic membrane which supports the piston by seal-connecting the piston with the center potion; and, moreover, the cavity which stores the microswitch is filled with a sealing agent.
In two surfaces which function as the mounting surfaces, low small protrusions are convexly provided on at least two places of one side, and in the corresponding position of the other side, hole portions to fit the small protrusions are concavely provided. Further, the plate spring is formed by polyimide, and the elastic membrane is formed by a disc bellows having an inclination along a flat conical surface with polyimide as a raw material. Further, the actuator lever is formed by stainless steel (SUS304) and the surface thereof is subjected to nitriding processing. In addition, a top end of the actuator lever is extended to the housing side, and a square hole which controls a moving range is piercingly provided at a position facing the housing side so as to idly fit to a protrusion of the housing side. On the other hand, a compression coil is insertably mounted between the piston and a mounting board of the microswitch and supports a weight of the piston and an urging force by the elastic membrane. Further, the mounting board of the microswitch is provided with an external thread on an outer periphery thereof and screwed into an internal thread provided on a piercing hole of the housing, and the mounting board of the microswitch is rotated so as to move a position relative to the actuator lever by a screw mechanism and a distance of an operating position by the actuator lever for a free position of the microswitch is made adjustable.